The research is concerned with the study of the structure and function of creatine kinase isozymes. Creatine kinase plays an important physiological and catalytic role in muscle and cerebral energy metabolism. However, although ATP is considered to be the intermediate source of chemical energy in the muscle and the brain, a major reservoir of readily available chemical energy is creatine phosphate, a product of the reaction catalyzed by creatine kinase. The study consists of two parts, namely, (1) determination of the three-dimensional structure of the enzyme, and (2) study of the enzymatic and spectral properties of the enzyme labelled with mercurinitrophenol, a dynamic, conformation-dependent spectral probe. Both the spectral perturbations of the enzyme-bound nitrophenol illicited by the binding of substrates, singly or in combination, and the rates of reaction of the probe with the liganded and unliganded enzyme are sensitive indicators of the dynamic property and varied conformation states of the enzyme.